Image plate scanner

ABSTRACT

An improved image plate scanner (10) for scanning a circular videodisk (12) exposed by X-rays, with image elements (40) spaced a distance (radius R) away from the image plate central point. The image plate is scanned with laser beams. A videodisk carrier (13) on which the image plate is detachably mounted, is drivable with the aid of an electromotor (11), with adjustable rotation speeds. An image element scanning unit (15;115) is radially displaceable across the image plate by means of a drive assembly (14,18) with presettable speed of advance. A laser light supply (42) and an optical image element scanning facility (30a) are parts of an optoelectronic measured value transmission unit, as are a photomultiplier (36) and a signal conditioner. During the light scanning for recording the image stored on the image plate maximum light yield is obtained for the emitted light. The image plate scanner is constructed in a compact manner so as to facilitate operation. The image element scanning unit (15;115) can be guided across the image plate while scanning each image element ( 40) at the same tangential speed, provision being preferably made for the laser light supply (42) to include a collector lens (44), two laser light sources (43a,43b), and an optical filter (46) by means of which the laser light is focussed. The drive shaft (18) of the electromotor (11) is connected by a gear drive to a power spindle (26). The image element scanning unit (15) is translatorily displaceable radially over the image plate (12).

SCOPE OF APPLICATION

The present invention relates to an image plate scanner for a device forscanning an image plate exposed by X-rays with the aid of laser beams.

STATE OF THE ART

From the EP-A-144 856 it is known to expose image plates in which, on asubstrate material, a stimulable phosphor layer of BaFEu:X-crystals isdisposed in a binding agent with the aid of X-rays. The recording of theX-ray image is effected by the action of the X-rays on theBaFEu:X-crystals. For the image plate scanning, the image plate isscanned with laser light, whereby the different quantities of X-raysabsorbed by the image plate are converted into light possessingequivalent intensities. The light is then first converted into analogelectrical signals, then into digital signals, following which thedigitized image is processed further in a computer. The residual imagequantity remaining on the image plate subsequent to the image platescanning is then deleted in that the image plate is exposed to light.The thusly treated image plate can then be reused for image recordingwith the aid of X-rays. However, image plate scanners which are alreadyknown are subject to the disadvantage that the light yield in the imageplate scanner is impaired, due to the circumstance that the sensitivityof the image plate scanner is unsatisfactory for many fields ofapplication.

In order to improve the known image plate scanners, with the EP-OS 296365, an image plate scanning device is proposed in which an image platein the form of a circular plate is disposed on a rotatable disk carrier,the image plate being in this case constructed so as to be suitable forthe storage of a beam image. The image plate carrier is provided with anelectromotor having adjustable speeds, on whose drive shaft the imageplate is detachably mounted. The image plate is scanned by means of animage element scanning unit while the image plate is in rotation, andthe image element scanning unit is made to travel radially across theimage plate at a preset speed of advance. In this case the image plateis subjected to radiation by a laser light from an He-Ne laser as alight source, and the image element scanning unit records theluminescence produced by the image plate at every specific point and isconnected to a photomultiplier and a signal conditioning or preparationmeans. This image plate scanning device operates in such a way that theimage dots to be scanned are indicated in a polar system of coordinatesas a function of the radius R and the angle theta, and the pertinentintensities are detected with the aid of the image element scanningunit, while the speed of the frame supporting the image plate scanningunit is in a predetermined relationship to the rotational speed of theimage plate carrier. In this case it is always the ease that the imageplate scanning unit is displaced radially inwardly at a certain speedper rotation of the image plate so that the image plate is scanned inits entirety. Here the scanning is effected in concentric circles.

Since the velocity of the image plate is not changed, the closer theimage element scanning unit approaches the central point of the imageplate, the duration of the scanning per image element becomesincreasingly longer radially form the outside toward the inside, i.e.the recording times within the outer area are extremely short. The driveassemblies for the image plate and for the radial adjustment of theimage element scanning unit are independent of each other so that it isnot ensured that, when scanning image plate to be compared, the scanningis invariably begun at the same starting point. This would lead to thegeneration of dissimilar scanning results.

Also in the devices proposed in the FR-A-34 38 300 and in the JP-Sho63306760, spiral scanning is provided, however, no provision is made foruniform scanning. From the DE-OS 30 14 433, an assembly for the scanningof masters provided with graphic patterns is known, in which it ispossible to determine the position of image dots of pixels with a greatdegree of accuracy because provision is made for the scanning carriage,which is displace along predetermined straight scanning lines, to beequipped with two scanners which can specific marks on clocking rulersso as to make it possible that an allocation of the scanned marks to thegenerated signals can take place. A image plate rotational positioncoder or a image plate radius coder is not provided in the assemblyaccording to this publication.

TECHNICAL PROBLEM, SOLUTION, ADVANTAGES

It is the object of the invention to improve an image plate scanner ofthe type stated above in such a way that, during the light scanning forrecording the image stored on the image plate, as large as possible alight yield is achieved for the emitting light, in which case the imageplate scanner should be constructed in a compact manner so as tofacilitate the operation.

According to the invention, the solution of the technical problem isbrought about by means of an improved image plate scanner. With the aidof this improved image plate scanner, optimal scanning and recording ofan image plate takes place, since the adaptation of the speed to thekinematic conditions is effected in such a way that each image elementis scanned at the same tangential speed. The central concept in thiscase is that the image element scanning unit is passed across the imageplate in dependence on the radius R of the respective image element andin such a way that all scannable fields are swept over at the samespeed.

DESIGN OF THE INVENTION

Preferred embodiments and further developments of the invention are setforth below.

Provision is made in this connection for it to be possible for the imageelement scanning unit to be passed rapidly across the image plate at avelocity which is inversely proportional to the radius R of therespective image element and/or that the image plate can be driven at arotational speed (rotational position speed) which is inverselyproportional to the radius R of the respective image element.

Moreover, by preference, a rigid coupling is provided between thescanning motion and the rotational motion of the image plate so as toensure a starting point which is the same at all times. In addition, bypreference, the employment of two lasers is proposed in order to providea compact and inexpensive device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following description the invention will be explained in greaterdetail with reference embodiments of an image plate scanner that areschematically illustrated in the drawings. Thus

FIGS. 1-3 show, in a front view, a top view and a fragmentary side view,respectively, a further construction of an image plate scanner indiagrammatical depiction;

FIG. 4 is a functional block diagram of the image plate scanneraccording to FIGS. 1 to 3;

FIG. 5 is a diagrammatical illustration of the functional level of animage plate scanner;

FIGS. 6 and 7 are diagrammatical illustrations of the approximation ofthe image element length;

FIG. 8 shows a diagrammatical illustration of the image elementtransformation;

FIG. 9 shows a three-dimensional profile of the scanning speed;

FIG. 10 graphically depicts the scanning speed, and

FIG. 11 shows the rotational speed pattern during the scanning operationof a an image plate;

FIG. 12 is a diagrammatical illustration of the optical system of animage element scanning facility for the image plate scanner;

FIG. 13 shows, from the front, in a diagrammatical view, an image platescanner in a detail drawing;

FIG. 14 shows the image element scanning unit in a side elevation;

FIG. 15 shows, in a section, the reflector of the image element scanningunit in an enlarged side elevation, and

FIG. 16 shows a device for the scanning of a an image plate with animage plate scanner according to FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE OF IMPLEMENTING THEINVENTION

In FIGS. 1 to 3, a first embodiment of the image plate scanner 10 on abaseplate 100 on a retaining frame 110 is diagrammatically depicted. Theimage plate scanner 10 is provided with an electromotor 11 as drivingmotor which sets an image plate carrier 13 with a stimulable phosphorimage plate 12 thereon into rotation and moves the image elementscanning unit 15 in a translatory manner by means of a toothed beltdrive 14. The electromotor 11 is connected to a tachogenerator 16 forcontrolling the rotational speed as well as for controlling a an imageplate rotational position coder 17. A toothed belt wheel 19 of thetoothed belt drive 14 is positioned on the drive shaft 18 of theelectromotor 11. The toothed belt 20 passes across two further toothedbelt wheels 21, 22, one of which is disposed on the shaft of a geardrive 23 constructed in the form of a worm gearing 24. This worm gearing24 is connected to the power spindle 26 of the image element scanningunit 15 by means of a flexible coupling 25. The same is guided by meansof a head support 27 on two guide rails 28, 29. The power spindle 26passes through the head support 27. By displacement of the head support27, the image element read head 30 is made to travel radially inwardlyacross the image plate 12 in such a way that the radial speed of advanceis proportional to 1/radius R.

FIGS. 4 and 5 illustrate the control sequence when the video scanner 10is operated. The rotation speed generator 31 is activated by means ofthe image plate rotational position coder 17 which, by means of a servoamplifier 32, activates the electromotor 11 which is connected to thetachogenerator 16. The image plate rotational position coder 17 isfurther connected to the pixel apportionment generator 33 which isconnected with an integrator 34 and with a digitizer 35. With the aid ofthe digitizer 35, the analog measured values of the photomultiplier 36are converted into digital measured values of the image elements 40(FIGS. 6 and 7) determined by special scanning of the image plate 12 andare processed further by means of an interface 37 (FIG. 5) in theevaluating unit 38. The operational sequence is in this case controlledby a control unit 39, it being also possible to carry out the threetasks of motor control, control and separation of the image elements,and signal conditioning or editing in an integrative manner.

The basic problems involved in the scanning of a circular image platealong a spiral, and the technical solution thereof are diagrammaticallyexplained with reference to FIGS. 6 to 8. As the image elements 40 arescanned, the image element widths are reduced in size with a diminishingradius. For that reason an increase in the widths of the image elementsoccurs in that, with a diminishing radius R, an increase of therotational angle takes place (FIG. 6), which laterally delimits therespective elements 40. from this, with a decreasing radius of thespiral scanning operation, image elements 40 which possess differentsizes result (FIG. 6). In the evaluating unit 38, by means of analgorithm, the spiral image dots are then converted into image dots of aCartesian system of coordinates (FIG. 8). This may be effected in eitheran infinitesimal or a geometrical manner. Due to the invariabilities ofthe surface transformation, these are to be effected only once, in whichconnection it is possible to reuse the results in a tabulated list.

In the FIGS. 9 and 11, the pattern of the rate of advance of the imageelement scanning unit 15 is illustrated. The rate of advance begins at alower value in the circumference of the image plate 12 and rises up to amaximum within the area of the central point (FIG. 13) of the imageplate 12. The image element read head 30 is first made to approach theimage plate 12 and, with an increase in the rotation speed for a briefperiod, is brought to the starting point 41 (FIG. 11). From here thechange in rotation speed proceeds as depicted in FIG. 10, until theimage element read head 30 has reached the area of the central point ofthe image plate 12. In the video scanner 10, the direction of rotationof the electromotor 11 is then changed, and the image element read head30 is withdrawn at high speed across the image plate 12 (FIG. 11). Atthe same time, the residual quantity of light on the image plate 12 canbe eliminated with the aid of illuminators.

On account of the inversely proportional dependence of the rate ofadvance on the radius, it is possible to achieve a constant scanningspeed for each image element 40 of the image plate 12. Since thephotomultiplier 36 and the parabolic reflector 52 (FIG. 12), whichserves as light collector, move together with the means which emits thelaser light, a maximum light yield is achieved for the light emittedfrom the image element 40. The use of two laser light sources inconnection with a joint collector lens 47 is also of advantage since, ina compact model of the image plate scanner 10, the yield of the lightscanning is significantly increased thereby. The measured valuesobtained by the spiral scanning of the image elements 40 are, with theaid of a conversion algorithm, converted from spiral coordinates intomeasured values of Cartesian coordinates. In the signal processing it istaken into consideration by means of approximation that the size of theimage elements 40 across the image plate 12 is not constant, since thechange of radii between the rings of the measuring spirals remainsconstant. The desired information that may be determined with the aid ofthe processing is the integrated intensity of the light per imageelement 40. The aim is the maximum utilization of the emitted light ofthe image plate 12. For the integration of the signal, a gate-controlledintegrator is preferably used. No preamplifier is employed in order toprevent boosting of the background noise.

It is also possible, in lieu of analog control of the electromotor 11,to construct the same in the form of a stepping motor. In this case itwill be necessary that no stepping losses occur and that, subsequent tothe acceleration to the starting speed having taken place, no vibrationsoccur in the entire system. In this case, the stepping motor may becontrolled with the aid of a quartz oscillator having a fixed or avariable series of pulses.

The optical system of the image element scanning unit 15 is showndiagrammatically in FIG. 12. The laser light supply means 42 includestwo lasers 43a, 43b, whose laser light is passed through a pinholediaphragm 44. The laser light beams 45 pass through a filter 46 whichmay be constructed in the form of a red filter, e.g. of the type OG 590.This filter serves to hold back blue laser light components. The laserlight beams 45 which pass through the filter 46 are focussed by means ofa collector lens 47. The collector lens 47 may be provided with acoating in order to eliminate reflections and is expedientlydisplaceable in the axial direction so as to make it possible to changethe diameter of the focus. The laser light issuing from the collectorlens 47 is deflected by means of an adjustable deflector mirror 48,which is constructed so as to be highly reflective, and conveyed throughthe perforation 49 of an ultraviolet-reflective mirror 50, as well asthrough a perforation 51 of a reflector 52.

It is possible to dispose the lasers 43a, 43b, the pinhole diaphragm 44,the filter 46 and the collector lens 47 on the frame 110 of the imageplate scanner 10 and to supply the laser light beams 45 via thedeflector mirrors 53 of the image element scanning unit 15, or else theymay be mounted stationarily within the housing of the image elementscanning unit 15. The optical image element scanning facility 30a (FIG.13) is comprised of the reflector 52, the mirror 50 and thephotomultiplier 36. An optical filter 54 is inserted before thephotomulitplier and consists of two blue filters 55, 56, e.g. of thetype BF 12, BG 3. With the aid of this filter 54, red light componentsof the light reflected by the image plate 12 are filtered out. Bypreference, the inner wall of the reflector 52 is constructed so as tobe polished. The reflector 52 may, in its cross-section, be parabolic,elliptical or otherwise of cylindrical constructional configuration.

In the FIGS. 13 to 16, a further embodiment of an image element scanningunit of an image plate scanner is illustrated.

The FIG. 13 shows an image element scanning unit 115 as well as a imageplate 12 in a top view. The image element scanning unit 115 is providedwith a frame 60 which is radially displaceable across the image plate12. The laser light supply means 42 and the optical image elementscanning facility 30 are constructed within the frame 60. By means ofthe image element read head 30, it is possible to scan one image element40 of the image plate 12 at a time. The image plate 12 is rotatablysupported. With the aid of an indicated image plate rotational positioncoder 17 and the angular value generated therefrom and the number of thezero passes or transits of the image plate 12 of the radius R of theimage element 40 calculable on the basis of constant advance, themeasured values of the local fixation of each image element 40 can besupplied to the evaluating unit. An He-Ne laser may be employed as thelaser. In the depicted embodiment, the laser light supply means 42 is ofa two-piece construction, the laser light being deflected between thetwo parts with the aid of two mirrors 61.

In the FIG. 14, the image element scanning unit 115 according to FIG. 13is depicted in a side elevation in section. The image element readinghead 30 of the image element scanning unit 115 includes the reflector52. As is shown in greater detail in FIG. 15, the reflector 52 isconstructed inside a reflector housing 52a, while a perforation 51 isconstructed in the tip 52b of the reflector 52. The perforation 51serves to allow the laser light to pass through to receive thephotooptical emissions of the crystals of image element 40 of the imageplate 12 which are acted upon by the laser light. The mirror 50 ismounted above the reflector 52 which serves to deflect the photoopticalemissions which enter through the perforation 51 on to thephotomultiplier 36. An optical filter 54 with the blue filters 55, 56,is fitted before the photomultiplier 36. A perforation 49 is constructedin the mirror 50 and serves to lead to laser light beam 45 through thesame. The laser light supply means 42 is mounted above thephotomultiplier 36, but may also be mounted on the side. By means of alateral disposition it is possible to reduce the constructional heightof the image element scanning unit 115. The laser light supply means 42is also in this case advantageously acted upon by two laser lightsources whose laser light beams 45 are supplied through the filter 46and the collector lens 47, by means of which the laser light beams 45are focussed, and, via a deflector mirror 48, are conveyed in aconcentrated beam through the perforation 49.

In FIG. 16, a further embodiment of an image plate scanner 10 isdiagrammatically illustrated (in part). In this case, the frame 70 ofthe image element scanning unit 115 is displaceable on a retaining frame110 by means of a stepping motor 71. The stepping motor 71 is connectedto a control unit 72, with the aid of which the pattern of the speed ofadvance of the image element read head 30 of the image element scanningunit 115 is controlled inversely proportional to the respective radius Rof the image element 40 of the image plate 12 by the determination ofthe respective rotational position from encoder 17 and the number of thezero passes (number of complete rotations), above which the imageelement read head 30 is located. The image plate 12 is located on animage plate carrier 13 which is mounted on the drive shaft of anelectromotor 11 which serves as driving motor and which is secured tothe retaining frame 110 or to the housing 120, respectively. The imageplate rotational position coder 17 is, by means of a measured valuetransmission line 73, connected to a pixel apportionment generator 74.Generator 74 is connected to an evaluating unit 38 constructed in theform of an electronic calculating unit which, in turn, is connected to acomputer 38a. The photomultiplier 36 is, by means of a currentintegrator 75, likewise connected to the evaluating unit 38. Through thelatter, by means of a digitizer (not shown), the quantities of lightpicked up by the image element read head 30 are processed in the form ofdigitized signals into a digitized image which reproduces the imagestored on the image plate 12. The pixel apportionment generator 74 andthe current integrator 75 may also be accommodated in a separateelectronic casing located outside the housing 120.

It is of advantage for the image plate rotational position coder 17 tobe mounted on the drive shaft 18 of the electromotor 11, as is shown inthe drawings. With this arrangement the rotational speed and the actualrotational angle phi is, if necessary, derived from a rotation speedgenerator 31 by means of the pulse signals of the image plate rotationalposition coder 17. The rotation speed profile which is inverselyproportional to the radius R, is on this occasion stored in a servomotorcontrol unit 76 within computer 38a in the form of a digital table andis compared with the actual value supplied by the tachogenerator 16,while a control signal is generated by the driving motor control unit 77and supplied to the driving motor 11.

We claim:
 1. An image plate scanner for laser beam scanning a circularimage plate that has previously been exposed to X-rays to form thereonimage elements spaced at radial distances from a central point of theimage plate, said image plate scanner comprising a image plate carrierfor carrying an image plate to be scanned; electromotor means forrotating said image plate carrier with an adjustable rotational speedwith the image plate detachably mounted thereon; an image elementscanning unit; a drive assembly for driving said image element scanningunit at a presettable speed of advance to radially displace said imageelement scanning unit across the image plate so that each image elementis scanned at a constant tangential speed; laser light supply means; andan optical image element scanner including optoelectronic measured valuetransmission means, a photomultiplier and signal conditioning means. 2.An image plate scanner according to claim 1, wherein said drive assemblydisplaces said image element scanning unit radially over the image plate(12) at a speed inversely proportional to the radius of the respectiveimage element being scanned.
 3. Image plate scanner according to claim 1or 2, wherein said image element scanning unit includes an image readhead and means for positioning said image read head for reading of animage element on the image plate, and wherein said drive assemblyincludes means for driving said image element scanning unit at a speedinversely proportional to the radius of the image element being scanned.4. An image plate scanner according to claim 3 further comprisingcoupling means rigidly coupling said electromotor means and said driveassembly, and wherein said drive assembly includes a gear driveconnecting said coupling means to said image element scanning unit toadjust the rotational speed to be inversely proportional to the radialposition of said image read head over an image element on the imageplate (12).
 5. An image plate scanner according to claim 3, wherein saidimage element scanning unit includes a servomotor and a control unit fordisplacing said image read head radially with a radial velocityinversely proportional to the radial position of said image read headover an image element on the image plate (12).
 6. An image plate scanneraccording to claim 1, wherein said laser light supply means includes twolaser light sources, a collector lens, and an optical filter (46), laserlight from said two laser light sources passing through said collectorlens and said optical filter to be focussed.
 7. An image plate scanneraccording to claim 6, wherein said collector lens is coaxiallydisplaceable relative to the laser light.
 8. An image plate scanneraccording to claim 1, wherein said signal conditioning means comprises acurrent integrator, a pixel apportionment generator, and a digitizer forthe digitization of images of image elements scanned on the image plate.9. An image plate scanner according to claim 1, wherein said imageelement scanning unit includes laser light deflection means fordeflecting light from said laser light supply means, and a housingfixedly mounting said laser light supply means.
 10. An image platescanner according to claim 1, wherein said image plate carrier includesa measured value receiver, and wherein said image element scanning unitincludes an image plate rotational position coder for reading saidmeasured value receiver.
 11. An image plate scanner according to claim10, wherein said image element scanning unit further includes a pixelapportionment generator for converting outputs of said image platerotational position coder into pixel signals.
 12. An image plate scanneraccording to claim 11, wherein said image element scanning unit furtherincludes a measured value transmission line coupling said image platerotational position coder to said pixel apportionment generator.
 13. Animage plate scanner according to claim 1, wherein said electromotormeans includes a tachogenerator and a rotation speed generator.
 14. Animage plate scanner according to claim 1 or 13, wherein saidelectromotor means includes a motor having a drive shaft, and whereinsaid drive assembly includes a power spindle and a gear drive couplingsaid drive shaft to said power spindle (26) to translatorily displacesaid image element scanning unit radially with respect to the imageplate (12).
 15. An image plate scanner according to claim 14, whereinsaid drive assembly further includes a worm gear drive, a first toothedbelt wheel mounted on said drive shaft, a second toothed belt wheelconnected to said worm gear drive, and a toothed belt coupling saidfirst and second toothed belt wheels.
 16. An image plate scanneraccording to claim 14, wherein said image element scanning unit includesa head support for supporting said image element scanning unit, andguide rails in engagement with said power spindle for guiding movementof said head support to move said image element scanning unit.
 17. Animage plate scanner according to claim 1, wherein said image elementscanning unit includes an image element read head, a reflector having atip with an aperture therethrough for passing laser light to imageelements on the image plate and for receiving photooptical emissionsfrom the image elements on the image plate, a first mirror mounted abovesaid reflector and on said photomultiplier, for deflecting enteringphotooptical emissions from the image elements, the mirror having aperforation for the laser light beam to pass through.
 18. An image platescanner according to claim 17, wherein said reflector has across-section of a paraboloid or an ellipsoid or a combination of both.19. An image plate scanner according to claim 17, wherein said laserlight supply means further includes a deflector mirror mounted above orat the side of said first mirror.
 20. An image plate scanner accordingto claim 17, wherein said reflector includes an optical filter disposedbefore said photomultiplier, and whereby said photomultiplier and saidcurrent integrator form an optoelectronic measured value transmissionmeans.
 21. An image plate scanner according to claim 1, wherein saidoptical image element scanner further includes an optical filter beforesaid photomultiplier.